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Studies on arrested development of Ostertagia ostertagi and Cooperia oncophora

1974; Elsevier BV; Volume: 84; Issue: 4 Linguagem: Inglês

10.1016/0021-9975(74)90046-2

1532-3129

J. F. Michel, M.B. Lancaster, C. Hong,

Nematode management and characterization studies

Stocks of Ostertagia ostertagi from five different sources and of Cooperia oncophora from four were used in experiments on the causes of arrested development. Paddocks were contaminated by calves infected with one stock of each species and subsequently grazed for short periods by test calves and the proportion of worms arrested at the early fourth stage was determined. The results indicated that arrested development was due to the action of environmental factors on the free-living stages and not to seasonal changes in the host or to changes in the relative numbers of larvae that were or were not capable of interrupting their parasitic development. Differences between stocks of larvae consisted not only of differences in the proportion of larvae capable of responding to signals from the environment, but also in the nature of the response. The nature of these signals was not precisely identified, but they do not appear to be simple. The changes which they induce in the larvae are spontaneously reversed after a time.